For me, I think it has to fall under between the Panzer IVD (or even the IIIF) or the Matilda II.
For the Panzer, that fact that they pretty much all had radios was a big help to the German tactics in France and Belgium, and how they were able to cut off the Allied forces so quickly.
On the other hand, by itself, I think the Matilda was a pretty good tank during the Battle of France, at least with the earlier models of the Panzers.
I also believe it was the British tank that led the counter-attack at Arras (please correct me if I'm wrong). Of course, it couldn't stand up the the 88mm cannon, but I think many tanks of WWII (especially on the Allied side), could stand up to the 88.

Panzerkampfwagen III
By the fall of 1940 the PzKpfw III was being armed with the 5cm/42 main gun. Older model PzKpfw III were upgraded to this standard when due for overhaul. A nice balance of firepower, armor protection, mobility and reliability. At 22 tons it was light enough to use most European road bridges of that era.

most unappreciated tank would be the Cruiser MK IV.
With 30mm armour it is certainly no worse than most german tanks in 1939-40. It has a better gun than the MK III German (OK, no HE but the armour pentetraion is almost in a whole other class). One of the best power to weight ratios for good speed and mobility, something the Matlita doesn't have. It does have a radio (if the PTB lift radio silence so they can be tuned.

poorly trained crews and or bad tactics can skew combat results so that a good (OK it wasn't GREAT) tank doesn't give good results.

Given equel crews it should best the German MK III but the MK IV may be better all around with the 75mm gun.
The French tanks, even with good guns, have too many limitaions with their one man turrets.

The BT 7 is faster, it's gun might be better but has a two man turret and no cupola or commander postion, also few radios.
T-28 is a bit slower, a larger target and on the early versions no better armour. The early 76mm gun wasn't that hot for anti armour work either.
The less said about the Japanese tanks in a tank duel the better. Any tank beats no tank for infantry support.

By the fall of 1940 the PzKpfw III was being armed with the 5cm/42 main gun. Older model PzKpfw III were upgraded to this standard when due for overhaul. A nice balance of firepower, armor protection, mobility and reliability. At 22 tons it was light enough to use most European road bridges of that era.

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Not much to add, I agree with your assessment Dave.
Its my opinion too that PzKpfw III was the best battle tank in 1939/40, while PzKpw IV with short barreled canon at that time was still used mainly in support role for which it was designed in the first place.

Panzerkampfwagen III
By the fall of 1940 the PzKpfw III was being armed with the 5cm/42 main gun. Older model PzKpfw III were upgraded to this standard when due for overhaul. A nice balance of firepower, armor protection, mobility and reliability. At 22 tons it was light enough to use most European road bridges of that era.

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afaik the Pz III with 50/42 was not in battles in '40. (and for true it's from julliett)

A lot of peaples tanks were unreliable. The Cruiser MK IV might have been a bit more than some others but in any retreat/rear guard action that last for more than a couple of days a lot of tanks are going to get left behind.
Check out the number of Tigers that were lost due to mechanical break downs.

As far as fire power goes. to keep things simple I will stick to the MGs.

British tanks use either a water cooled Vickers or a Besa gun. Feed from long belts they both have a sustained fire capability that is not matched by most other tanks. The Czech Pz 38 uses the same MGs. THe German tanks use the MG 34 but they may not have quite the same sustained fire capability.
The Italian tanks certainly don't, even if the guns are reliable using 24 round magazines does limit the amount of rounds that can be fired after a short period of time.
The Russian tanks use 60 round magazines and I am not sure their barrels will really permit hundreds of rounds a minute for several minutes.
Japanese are using 20 round magazines on their tank MGs.

Then there is the ammo supply. The MK IV cruiser carried 3750 rounds of MG ammo for the Vickers and probably close to that for the Besa.
This is more than some other tanks carried for their multipule MGs.

True the cruiser IV have a lot of ammo for the mg (maybe only the T-28 and B 1 bis have more ) but all the tanks with only a mg, commonly this is coaxial, need fire with gun and mg in same direction and this afaik it's not the best

If the second gun can move indepentently of the 1st MG and main gun, who is aiming it and how?
If it is the loader then he is not loading the main gun or tending to the 1st MG or he is spliting his efforts which reduces the effort of the tank as a whole.

Is one gun better than two? NO.
But 2 guns (or three) are not twice (or three times) as good as one.

I would go with the pzkfw 111 , the radio and the fighting compartment were better then anything anybody had , but its the tactics the germans used that really made the most of there tanks. the matlidas were slow yes , undergunned, yes, but I think it was a fine fighting tank. also, the french char b and somnu, i think i got it right, the name, were good tanks too but there crews and leaders didnt know how too fight a mobile war

Yes it was. However without a HE round it was a poor choice for a tank main gun. Tanks typically spend more time shooting at soft targets then at armored vehicles. That is especially true for a so called "Infantry Support Tank" like the Matilda II. You cannot take out enemy infantry with AP rounds.

The PzKpfw III was the best tank during 39'-40'. The three man turret and suspension system put it at an advantage, and the 3.7 cm KwK 36 L/46.5 was good enough for those early campaigns as well. The Panzerkampfwagen IV was really the better tank against all other targets besides tanks due to it's low velocity 75mm. The only reason why it was not the best in armor battles.

IMHO PzIVD was the best general purpose tank of those mentioned in Vincenzo’s first message. 3 men turret, good HE round, reasonable AP round for its time but low muzzle velocity, radio, mediocrity armour protection and fairly reliable.

As for tank vs tank combat, Matilda II. It also had 3 man turret, excellent armour protection, very good gun for anti-tank work, radio but no HE, not very reliable and slow.

Cruiser Mk IV was on paper more or less equal to PzIII E and F but was a rather unreliable as were all British tanks with Liberty engine, even if IIRC cruisers used in Greece were A9s and A10s.

British had also CS tanks, which at that time had 3” howitzer as armament, bit like PzIV in WM, it had HE and smoke ammo. At that time British counted mg as anti-infantry weapon and bullets of Besa went through German A/T gun shields at distances which were normal battle distances in 39-40.

If the second gun can move indepentently of the 1st MG and main gun, who is aiming it and how?
If it is the loader then he is not loading the main gun or tending to the 1st MG or he is spliting his efforts which reduces the effort of the tank as a whole.

Is one gun better than two? NO.
But 2 guns (or three) are not twice (or three times) as good as one.

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agree
some note:
all but japanese have coaxial mg
the Pz III F have no more 2 mg in turret
add the mg eas the only anti infantry weapons on btritish tanks

British had also CS tanks, which at that time had 3” howitzer as armament, bit like PzIV in WM, it had HE and smoke ammo. At that time British counted mg as anti-infantry weapon and bullets of Besa went through German A/T gun shields at distances which were normal battle distances in 39-40.

my list is not closed all the tanks (that were in battles in '39/40) are challengers, i choice the best for country almost afaik (a put out the polish 7tp first for a error, however theuyare inferior a many tanks in the list)